Tone analysis system with visual display

ABSTRACT

An audible tone identifier comprises a transducer and amplifier for responding to audible tones, such as generated by a human voice speaking or singing, or a musical instrument, and a plurality of filters sharply tuned to the notes of one or more octaves or fractions thereof of the equal tempered chromatic musical scale or to other patterns of sounds that are to be individually identified. The outputs of the filters are connected to lamp driver circuits which in turn are connected through transposing plug-and-jack connectors and sharp-and-flat insertion switches to lamps on a display board, whereby any musical tone within the range of the device, received by the transducer, will be identified visually on the display board by the lighting of a lamp. The tone identifier may be a component of a teaching or speech therapy system including a source of recorded instructions and sounds to be produced by a trainee, such as a tape player and pre-recorded tape, and headphones through which the trainee hears instructions as well as the sounds produced by him. The relative conformity of tone frequencies with the center frequency of the filters is indicated by comparing the phase of said waves at the input and output of the filters.

United States Patent [191 Humphrey et a1.

[ TONE ANALYSIS SYSTEM WITH VISUAL DISPLAY [75] Inventors: Thomas D.Humphrey, Silberado; John H. Humphrey, Los Angeles, both of Calif.

[73] Assignee: Sound Sciences Inc., Santa Ana,

Calif.

[22] Filed: Aug. 30, 1973 [21] Appl. No.: 393,033

Related U.S. Application Data [63] Continuationdn-part of Ser. No.299,189, Oct, 20, 1972, abandoned.

[52] U.S. Cl 179/1 SA; 179/1 D; 84/477 [51] Int. Cl. G09B 15/02; GlOL1/00 [58] Field of Search 179/1 SA, 1 SP, 1 D; 84/477, 454; 35/35 C;324/83 R, 83 A, 83 D [56] References Cited UNITED STATES PATENTS2,181,265 11/1939 Dudley 179/1 SP 2,646,465 7/1953 Davis et al.....179/1 SP 2,779,920 l/l957 Petroff 84/454 3,180,201 4/1965 Low et 84/477R 3,384,818 5/1968 Longerich et al 324/83 A July 8, 1975 5 7] ABSTRACTAn audible tone identifier comprises a transducer and amplifier forresponding to audible tones, such as generated by a human voice speakingor singing, or a musical instrument, and a plurality of filters sharplytuned to the notes of one or more octaves or fractions thereof of theequal tempered chromatic musical scale or to other patterns of soundsthat are to be individually identified. The outputs of the filters areconnected to lamp driver circuits which in turn are connected throughtransposing plug-and-jack connectors and sharp-and-flat insertionswitches to lamps on a display board, whereby any musical tone withinthe range of the device, received by the transducer, will be identifiedvisually on the display board by the lighting of a lamp. The toneidentifier may be a component of a teaching or speech therapy systemincluding a source of recorded instructions and sounds to be produced bya trainee, such as a tape player and pre-recorded tape, and headphonesthrough which the trainee hears instructions as well as the soundsproduced by him. The relative conformity of tone frequencies with thecenter frequency of the filters is indicated by comparing the phase ofsaid waves at the input and output of the filters.

3 Claims, 8 Drawing Figures SHEET PMENTEM" WSQMUQ PATEN EB JUL 8 I975SHEET i u M M n. #IIKV mu wk w\ R I V N a 6% lTO h \E u $L H \k m. NN r1 1 l 1 1 1 1 I I I E I i l f l b E E I F t i k E I t I I i l E i I ilLI kl SHEET PATFHTFUJUL r ms TONE ANALYSIS SYSTEM WITH VISUAL DISPLAYRELATED APPLICATION This application is a continuation-in-part of ourapplication Ser. No. 299,189 filed by us on Oct. 20, 1972, nowabandoned.

BACKGROUND OF THE INVENTION Aids to the teaching of music, whether vocalor instrumental, and for the tuning of instruments have, in the pastgenerally employed one or the other of two concepts. In accordance withone of these concepts of the tone identifying device is comprised of aplurality of tone generators each of which may be individually activatedto generate a tone of known frequency. A tone originating in a musicalinstrument or in the vocal cords of a voice trainee is fed into thedevice through a microphone and amplifier and is applied to comparisoncircuitry, such as a cathode ray tube, along with the tone that is beinggenerated as selected within the device. Identification of the tone thatis being generated externally and applied to the device is thenaccomplished through a comparison and matching technique which is atbest an indirect method providing no useful output until a match hasbeen accomplished and therefore not giving a direct indication of toneidentity nor lending itself readily to the identification of two or moretones simultaneously sounded nor the possibility of a steady and lastingindication of the externally generated tone when the production of thattone has ceased.

The other concept involves the employment in the tone identifying deviceof a plurality of tuned vibratory elements such as reeds or tuningforks. These are tuned to the frequencies of the notes of the musicalscale and are arranged to be set in sympathetic vibration eitheracoustically or electrically, in response to an externally generatedtone that is to be identified and that is introduced into the devicethrough a microphone or other type of transducer. Petroff U.S. Pat. No.2,779,920, granted Jan. 29, i957, is an example of an audiofrequencymeter employing tuned reeds. A laminated iron core is arranged toinfluence all of the tuned reeds magnetically and the core carries awinding upon which are impressed the tone signals that are to beidentified. In one embodiment the reeds are arranged to serve as lightshutters and in another embodiment they are ar ranged to complete, intheir vibratory excursions, the circuits of lamps.

The tone display device employing tuning forks is disclosed in BalamuthU.S. Pat. No. 3,204,5l3, granted Sept. 7, I965. In this disclosure tonesto be individually identified by the lighting of lamps are applied to aplurality of windings each associated with one of a set of tuning forksto set the tuning fork in vibration at its natural frequency through aniron core associated with the winding. Each tuning fork also hasassociated with it a pickup coil to be energized at the frequency atwhich the tuning fork is vibrating. Each of the pickup coils controls acircuit closure device for completing a circuit of a lamp individual tothe pickup coil and therefore representing the tuning fork that has beenset in vibration.

Tone identifiers employing mechanically vibrating tone identifyingcomponents have significant shortcomings. Considering first the problemsinvolved in the employment of reeds, they are likely to bepositionsensitive, by which is meant that they may be more responsive toa tone stimulus in one position, such as a vertical position, than theyare in another position, such as a vertical position, than they are inanaother position such as a horizontal position. Moreover, minor changesin position, such as due to jarring, or major changes, such as due totilting of the structure suppporting the reeds, is likely to produceerroneous indications. Another disadvantage in the use of vibratingreeds is that they are subject to a hysteresis-like manifestation. Thereeds have been found to respond more effectively when activated in anascending sound spectrum sequence than they do when activated in adescending sequence. Reeds cannot be made to exhibit a high O, which isa figure of merit related to a factor of rejection of frequencies belowand above the frequency that they are intended to pass. Moreover, theycannot be produced practically to exhibit desired values of O at anyfrequency.

Reeds have poor dynamic range because sensitivity is limited at the lowfrequencies and linearity can be achieved only over a very narrow range.The inertia that characterizes mechanical vibratory devices introducesanother undesirable effect when those devices are employed as toneresponsive components of a tone identifying apparatus, the undesirableeffect being that the tone must be sustained until vibration of the reedor fork builds up to useful amplitude. At higher frequencies reedsbecome very short and the amplitude of displacement becomes so smallthat operation of light shutters or opening and closing of electricalcontacts cannot be accomplished. Moreover, vibratory objects such asreeds are subject to fatigue in the material of which they are made, andthe result is that a tone identifier employing reeds that is subjectedto substantially constant usage, as in the training of music students orin speech therapy, may require undesirably frequent replacement ofreeds. As a corollary of this, electrical contacts used to open andclose electrical circuits do not have unlimited useful or effectivelife, among the limiting factors being wear and other degradation, suchas pitting. When the contacts are reeds vibrating at voice frequenciesthe limit may be reached in a very short time, a matter of a few hours.It is not unusual for electrical contacts to fail after making andbreaking a few million times, perhaps 10 million. A vibratory reed tunedto operate 440 cycles per second, which is the frequency of A abovemiddle C in the musical scale, reaches 10 million operations in a fewhours.

SUMMARY OF THE INVENTION In the preferred embodiment of the presentinvention tones to be identified are impressed upon the tone identifyingdevice by means ofa microphone or other trans ducer, are amplified,shaped and set to an optimum level and are then impressed on the inputsto a plurality of filters. The filters are individually arranged to passone of the tones of a musical scale, either diatonic or chromatic, ofany desired number of octaves or fractions of octaves. The output ofeach filter is connected to the input of a lamp driver circuit and acontrol is provided whereby the lamp driver circuits will be activatedonly as long as a tone is being passed through the associated filter oralternatively will be locked in the activated condition so as tomaintain an indication after the tone that has activated the lamp drivercircuit has ceased. The outputs of the lamp driver circuits areconnected through transposing plug-and-jack combinations to multi-pole,multi-throw sharp-flat matrix switches and thence to lamps located on adisplay board. With the transposing plug-and-jack sets interengaged innon-transposing relation, and with the sharpflat matrix switchesadjusted to the natural condition of the tones the outputs of the lampdrivers are connected straight through the lamps on the display board,there being a lamp for each filter circuit and lamp driver in thedevice. Upon the generation ofa tone in the vicinity of the microphonethe fundamental of the tone, if on pitch, will be passed by one and onlyone of the filters, the filter that is tuned to that pitch and theassociated lamp driver circuit will be activated to cause the lightingof the lamp representing that tone. If the locking control for the lampdriver circuits has been set to lock those circuits when operated thetone indicator lamps will remain lighted after the tones that causedthem to be lighted have ceased; otherwise each lamp will be turned offwhen the tone ceases. If the shaping circuitry provides for thetransmission of overtones, other lamps may be lighted in response toharmonics.

Preferably the display board carries a representation of a musical staffcomprised of lines and spaces and carrying a clef symbol appropriate tothe musical notes that the device is arranged to identify, oralternatively a representation of the black and white keys of a keyboardinstrument. The lamps representing the various notes may be containedbehind the display board so as to be visible through windows in thatboard. Because the device includes lamps for the notes in a chromaticscale whereas the lines and spaces of the staff in accordance with theusual musical notation will accommodate only the notes of a diatonicscale, other apertures or windows above and below those for the naturalsof the notes may reveal the lamps representing the sharp and flatmodifications of the notes involved in diatonic scales other than thatofC Major. in the case ofa representation of a keyboard, the aperturesmay be aligned with the corresponding key representations.

The transposing plug-and-jack combinations enable the shifting upwardlyor downwardly of all of the lamps on the display board relative to theirdriver circuits, thereby to render the device useful in connection withtransposing types of instruments, such as clarinets, saxophones and somekinds of horns, which the musician manipulates in a mode which he istaught represents the key of C, the instrument sounding, however, in akey other than C and in the case of instruments of a family, such asclarinets or saxophones the instruments of different sizes or rangessounding in different keys although identically manipulated. Thetransposing plug-and-jack combinations permit transpositions as betweenwritten music and voice ranges necessitating the singing of acomposition in a different key.

The sharp-flat matrix switches permit the lamps pertaining to a singlenatural tone and its sharp and flat variations to be shifted inaccordance with a sharp or flat setting of the switch, to aid studentsin remembering sharp or flat notes called for by the key signature.

in addition to lamps a more precise indication of exact tone productionmay be provided, in the form of phase detector common to all of thefilters. inherent in the tone identifying filters is the fact that whenthe filter passes a tone that matches exactly the resonant frequency ofthe filter, the signal at the output of the filter is out of phase withthe signal applied on the input to the filter. If a tone which is sharpor flat relative to the resonant frequency of the filter is passedthrough the filter the phase difference will be on one side or the otherof 180. The detector is arranged to indicate deviation as a percentagedifference from the resonant frequency.

In addition to usage of the tone identifier alone and purely as a tonedisplay device, it is contemplated that the device may be part of ateaching or voice analysis system which includes as additionalcomponents a headset to be used by the subject and a source of recordedlesson or training material, such as magnetic tapes and a tape player.The headset is connected to reproduce the instruction material on thetape including musical notes by name to be voiced by the student intothe microphone, or actual tones that the student hears and is instructedto imitate. The tone identifying display panel informs the student as tosuccess or lack of success in following instructions, and the tonesvoiced by him may be heard through the headphones.

SUMMARY OF MUSICAL SCALE STRUCTURES Before entering upon a detailedconsideration of the preferred embodiment of the invention a backgroundreview of musical scales and musical notations may be helpful. Musicalscales are generally identified either as diatonic or chromatic. Thediatonic scale is divided into octaves, each octave containing sevennotes designated by the letters A through G in ascending order, and aneighth note designated by the same letter as the first note of thescale, distinguishable from the first by its location on a musical staffor by a subscript or other distinguishing mark associated with itsdesignating letter and having a frequency which is twice that of itscounter-part at the other or lower end of the octave. Beginning with anykey designating the note C on a keyboard instrument the diatonic scalein one octave is represented by the next six white keys in ascendingorder and closing the octave with the key representing the next note C.

The chromatic scale, on the other hand is a twelve note scale comprisedof the seven notes in the octave of a diatonic scale and five additionalnotes which, on a keyboard instrument, are represented by the five blackkeys intervening some of the white keys in an octave. The intervalbetween any two successive notes in a chromatic scale is generallydesignated as a semi-tone or half tone. With two exceptions the intervalbetween two successive notes of a diatonic scale is designated as twosemi-tones or a whole tone interval, and under that circumstance thereis a tone of the chromatic scale intervening the two, which would be thecase where there exists a black key between two adjacent white keys on akeyboard instrument. The two exceptions to this pattern are that thereis only a semi-tone interval between the notes B and C and between thenotes E and F, and this is evidenced by the fact that on a keyboardinstrument there is no black key intervening the keys representing andnotes B and C and the notes E and F. It follows from this that in anymajor diatonic scale the intervals between notes expressed by count ofsemi-tones are two, two, one, two, two, two and one. Another and moreusual way of expressing these intervals is that they are designatedwhole, whole, half, whole, whole, whole and half. Another way of viewingthe diatonic scale is that it is comprised of two tetra-chords separatedby a whole tone interval and including identical patterns of intervals,namely, whole tone, whole tone, half tone.

The notes of the chromatic scale corresponding to the black keys of akeyboard instrument are designated as sharp or flat relative to thenotes of the diatonic scale that they intervene. Thus the note betweenthe notes F and G is designated either as F sharp or G flat, andsimilarly the note intervening the notes A and B is designated either Asharp or B flat. Because the scale of C Major does not include any ofthe notes corresponding to the black keys of a keyboard instrument, itskey signature in musical notation contains neither sharps or flats. Avocalist singing the scale of C Major calls the tonic note C by thefamiliar designation do and the remaining notes in ascending order asre", mi", "fa", "so", "la", ti", completing the octave with do".

Other major scales are derived by the substitution of black-key" notesof the keyboard instrument for their natural or white-key" counterparts,and this is accomplished in musical notation by key signatures includingone or more sharps or flats. Five sharps or five flats will bring into amajor scale all of the black-key notes, and the sharps or flats are usedcumulatively in the key sig natures. In the case of sharps they areapplied cumulatively to the notes F, C, G, D and A and these produce themajor scales of G, D, A, E and B respectively. In the major scalebeginning with each of these letters the intervals between notes arethose hereinbefore mentioned, and for a vocalist singing in any one ofthese major keys the first note or tonic of the scale, which is the notefrom which the key derives its name, is identified as do." There arealso key signatures including six and seven sharps and these are appliedto the notes E and B, and raise those notes by a semi-tone. Since, aspreviously stated, the interval between E and F and between B and C is asemi-tone, the tone represented by E sharp is actually the tone of Fnatural and the tone B sharp is the same as the tone C natural. Lookingback at the sequence of addition of sharps it will be noted that thefirst two sharps eliminate the notes F natural and C natural from thescale, so that no problem arises in later designating these notes as Esharp and B sharp respectively.

Flats all also applied cumulatively to derive other major scales and thesequence of addition of flats is B, E, A, D and G to substituteblack-key notes as flattings of their white-key counterparts and therebyderive the major scales having the tonics F, B flat, E flat, and D flat.Sixth and seventh flats added to the first five, and applied to C and Fproduce major scales beginning on G flat and C flat. As in the case ofthe sixth and seventh sharps the addition of the sixth and seventh flatsresults in the flatting of the notes C and F which are only a semi-toneinterval above their next lower notes in the scale and the tones soundedfor the notes C flat and F flat are the same as the tones for the notesB natural and E natural. Also, as in the case of the sixth and seventhsharps, the first two flats eliminate B natural and E natural from thescales having flats in the key signatures, so that no problem arises inthinking of the notes B natural and as C flat and F flat respectively.It should be understood that the sharps or flats in key signaturesmerely substitute other notes for naturals and that the scalerepresented in musical notation by any key signature, whether the keysignature contains sharps, flats or neither, is a diatonic scale.

DESCRIPTION OF THE DRAWINGS For a complete understanding of theinvention reference may be had to the following detailed description tobe interpreted in the light of the accompanying drawings wherein:

FIG. 1 is a schematic representation of the circuitry of a visualdisplay device in accordance with the present invention;

FIG. 2 is a schematic representation of one of the sharp-flat switchesof the device;

FIG. 3 is a schematic circuit diagram of a lamp driver circuit;

FIG. 4 is a diagrammatic representation of a typical display panel;

FIG. 5 is a schematic circuit diagram showing the input circuitry of thetone identifier;

FIG. 6 is a graphical view showing a family of response curves of atypical band pass filter;

FIG. 7 is a schematic circuit diagram showing a typical filter employedin the tone identifier and a phase detector for monitoring the filters;and

FIG. 8 is a schematic circuit diagram showing the circuitry of ateaching and voice analysis system incorporating the tone identifyingdevice.

DETAILED DESCRIPTION Referring now to the drawings and particularly toFIG. 1 the reference numeral 10 designates a microhphone connected tothe input of an amplifier 12, the microphone 10 being provided forresponding to sounds from any source, such as the vocal cords of aperson or sounds generated by a musical instrument. The output of theamplifier 12 which is represented by the conventional triangular symbol,is connected to a swinger or movable contactor 14 of a double-poledouble-throw switch, and the terminals associated with that swinger areconnected to the inputs of a ramp preamplifier l6 and a wide passpreamplifier 18. The outputs of the preamplifiers 16 and 18 areconnected to the inputs of amplifiers 22 and 23 respectively. Theoutputs of the amplifiers 22 and 23 are connected to the terminalsassociated with the swinger 20 of the double-pole double-throw switchand that swinger is connected to the inputs of a plurality of filters tobe identified hereinafter. The swingers or contactors 14 and 20 of theswitch are ganged to operate together for the purpose of connectingeither the ramp preamplifier 16 or the wide pass preamplifier 18 to theplurality of filters.

The characteristic of the ramp preamplifier is that it has a risingattenuation with increasing frequency and its function is to attenuatethe harmonics of tones picked up by the microphone 10, so that only thefundamentals of the tones will have levels of sufficient amplitude toregister in the tone identifying circuitry that follows. The wide passpreamplifier does not similarly attenuate the harmonics and thus somemay have sufficient magnitude to register in the tone identifyingcircuitry in addition to their fundamentals. The switch comprising thecontactors I4 and 20 permits the selective passing of either type ofsignal.

The amplifier 22 is preferably a saturated amplifier, operating betweensaturation and cut-off so as to square the signals impressed upon it andit may include an output level control. The amplifier 23 does notsaturate nor cutoff, and it may also include an output level control. Aschematic circuit drawing of the ramp preamplifier and saturatedamplifier, as well as of other component apparatus in accordance withthe invention, is shown in FIG. and will be described in detailhereinafter.

The swinger of the double pole switch is connected to the input of eachofa plurality of filters designated in common by the reference numeraland individually by the musical note that the filter is tuned to pass.In addition there is shown in some of the representations of the filter30 the actual frequency of the note in accordance with the equaltempered scale, and it will be recognized that the showing in FIG. Icomprises an octave plus one additional note, that these notes are theones that in musical notation appear in association with the musicalstaff bearing the treble clef, and that the filters provide for thehandling of the tones of a chromatic scale. It will be understood thatthere may be provided any number of filters to receive tone signals fromthe amplifier 22 for a wide spectrum of tones or selected portions ofthe spectrum, including tones associated with ledger lines and spacesabove the treble staff, the tone for middle C associated with a ledgerline between the treble and bass staffs in the spectrum and for tonesassociated with the bass staff. The filters 30 may be of any circuitcomposition that will afford band pass characteristics of sufficientsuppression properties to pass the tone signals that they are intendedto pass and to reject the tone signals next above and below in thechromatic musical scale. A form of active band pass filter that issuitable for use as the tone identifying filters in the presentinvention is a multiple feedback network embodying the teachings of anarticle entitled Simple Arithmetic: An Easy Way to Design Active BandPass Filters that was published in the June 7, 1971 issue of thepublication Electronics beginning on page 86 of that issue and ending onpage 89, and that published disclosure is incorporated herein byreference as a part of the present specification. Additionally, aschematic circuit drawing of a filter suitable to the accomplishment ofthe desired result is shown in FIG. 6 and will be described in detailhereinafter.

It will be understood, of course, that filter is used here in itsgeneric sense, to designate any type of device that will distinguishamong or separate frequencies, including devices operating uponanalogue, digital and counting principles, and that there may be fewerfilters than display lamps, such as for example, one or more counterseach with logic circuitry to select one or another of several lamps foroperation depending upon the cumulative count within a given timeinterval.

The output of each of the filters 30 is connected to the input of a lampdriver circuit 32 which, as shown in FIG. 3 may consist of transistors34 and 36 having the base of the transistor 34 as the electrodecontrolled from the band pass filter, the transistor 34 being turned onto effect the lighting of a lamp to be identified hereinafter. Thetransistor 36 has its base connected to be driven by the transistor 34and has its collector connectable to operating voltage through amanually operable switch 38 that is common to all of the lamp drivercircuits 32. When the switch 38 is open the transistor 36 cannot beturned on and the lamp that is controlled by the transistor 34 will belighted only as long as the band pass filter that has been activated bya particular tone is receiving that tone. With the switch 38 closedhowever the transistor 36 will be turned on when the transistor 34 turnson and will in turn hold the transistor 34 turned on after thecontrolling input to the transistor 34 from its associated tone passfilter 30 has terminated. Thus the lamps may, if desired, be controlledto remain lighted after having been activated, this being accomplishedby the closure of the switch 38.

The output leads from the lamp driver circuits 32 are connected to amuIti-path plug-and-jack set designated generally by the referencenumeral 40 and. the paths are then extended to contactors or swingers ofsharpflat insertion control switches in a pattern which will behereinafter identified. The output leads from the sharpflat insertionswitches are connected on a one-for-one basis, relative to the lampdriver circuits 32, to lamps designated generally by the referencenumber 42. Additional multi-plug-and-jack sets, designated generally bythe reference numerals 44 and 46 may be included in the paths betweenthe lamp driver circuits 32 and the multi-path plug-and-jack set 40, andbetween the output side of the sharp-flat switches and the lamps 42, sothat the device may consist of modules to be interconnected through themulti-path plug-and-jack sets 44 and 46 whereby different arrangementsof control circuitry may be connected between the lamp drivers 32 andthe lamps 42 as special purposes may dictate. The multi-pathplug-and-jack set 40, however, has as its "function the transposing ofthe lamps 42 with respect to the lamp driver circuits 32.

FIG. 4 is a showning of a display that may appear on a panel inassociation with the lamps 42. The display contains a musical staff 50of five lines and four spaces carrying the G-clef 52 which indicatesthat the staff 50 is the treble staff, on which it is customary todisplay the notes E, G, B, D and F on the five lines from bottom to topof the staff and the notes F, A, C, and E on the four interveningspaces.

Apertures or windows 54 on the lines and spaces of the staff are alignedwith note indicating lamps 42 (FIG. I) and the apertures or windows havebeen designated in FIG. 4 by the note designations of the lines andspaces of the treble staff for the key of C.

The display panel is also provided with smaller windows or apertures 56,aligned vertically between the two vertical alignments of windows orapertures 54 and positioned in pairs in each of the four spaces betweenthe five lines. Behind the small apertures 56 are located those of thelamps 42 that represent sharp or flat notes of the scale corresponding,as previously mentioned, to the black key notes of a keyboardinstrument. The arrangement of the large and small apertures 54 and 56and the lamps located behind them is such that a lamp and its displaywindow representing the sharp of one natural note in the scale and theflat of the next higher natural note appears on a line passing throughthe centers of the apertures or windows representing the two naturalnotes in the scale.

Attention is now directed to the fact that in the array of lamps in FIG.1, a lamp appearing between those representing the notes E and F, andone appearing between the notes B and C, are designated E+ and 8+respectively. It has been set forth hereinbefore that the intervalbetween the notes E and F and between the notes B and C is a semi-toneand accordingly, there is no intervening note. It has also been setforth that when key signatures contain six and seven sharps or flatseither note of either of these two pairs of notes may be brought intothe musical scale as the sharp or flat of the other. The lampsdesignated E+ and B+ provide a dis play for this situation and these twolamps might also be considered as having a designation F and C.

FIG. 2 is a schematic showing of one of the sharp-flat insertionswitches. The switch is identified by the reference numeral 48 and is athree-pole, three-throw switch. As employed in the circuitry between thelamp driver circuits 32 and the lamps 42, as shown in FIG. I, the upperand middle switch terminals associated with the upper contactor 48-1 arestrapped together for the notes F, A, C and D, but the upper terminalassociated with the upper contactor is left unconnected for the othernotes namely E, G, and B. The middle and lower switch terminalsassociated with the lower contactor 48-3 of the switch are strappedtogether in the switches for the notes F and C only. In all of theswitches, the lower terminal associated with the upper swinger 48-1 theupper terminal associated with the lower swinger 48-3 and the middleterminal associated with the middle contactor 48-2 are strappedtogether.

Referring now to the switch designated F in FIG. 1, it will be notedthat the lower, middle and upper contactors 48-3, 48-2 and 48-1 of thatswitch are connected to the lamp drivers associated with the tone passfilters for the tones E, F and F sharp, respectively, the last mentionednote also having the designation G flat. The switch is set for thenatural note condition, when the three contactors are engaging theirmiddle terminals. From the middle terminals associated with contactors48-3, 48-2 and 48-1 of the F switch paths are extended to the E, F and Fsharp lamps, the first of these three including the middle contactor48-2 and associated middle contact of the switch for the note E, thesecond being a direct connection and the third including the lowercontactor 48-3 and middle contact of the switch 48 for the note G.

The path just traced accounts for the lower contactor 48-3 of the switch48 for the note G. The middle and upper contactors 48-2 and 48-1 of thisswitch are connected respectively to the lamp driver circuit 32associated with the filters 30 for the notes G and G sharp (A flat). Themiddle contact associated with the middle contactor 48-2 of the switch48 for the note G is connected to the lamp G and the middle contactassociated with the upper contactor 48-2 of the switch G is connected tothe lower contactor 48-3 of the switch for the note A which has itsassociated middle contact connected to the lamp for the note G sharp (Aflat).

Complete switch connections have been shown, in addition to thosealready described, for the switches for the notes A, B, C, and D. Theswitch connection for the switch E duplicate, relative to the lamps Eflat, E and E+, those of the switch B for the lamps B flat, B and B+ andhave been omitted along with those ofthe fragmentally shown switch forthe note F at the upper end of the octave.

It will be apparent from the foregoing that when all of the sharp-flatinsertion switches are in their natural" settings the activation of anyone of the lamp driver circuits 32 in response to its assigned musicalnote will result in the lighting of the lamp 42 corresponding to thatnote. The sharp-flat insertion switches when operated to their sharppositions, which is a movement of the contactors downwardly, or to theirflat settings, which is a movement of their contactors upwardly, is tochange the routing of paths from lamp driver circuits to lamps.

In order to understand how the insertion of sharps or flats may aidvoice or musical instrument trainees, it should be remembered that inmusical notation the key signature employing sharps or flats appear onlyat the beginning of a staff and it is necessary for the reader toremember this and to produce the sharp or flat variation of the note atthe time the note is encountered on a line or space of the staff, sincethe notes as they appear are not individually identified by the sharp orflat symbol.

The utility of the switches may be illustrated by assuming that astudent is producing tones being read from music written in the key ofGMajor which has one sharp, on the note F, in its key signature. Theinsertion of a sharp on F into the circuitry shown in FIG. 1 isaccomplished by moving the three contactors of the F switch down totheir lower contacts. All other switches will be left in their naturalpositions. This results in disconnection of the F sharp lamp from the Fsharp lamp driver, and connection of that lamp driver instead to the Flamp. The lamp driver for the note F becomes connected to the E+ lamp,but the E lamp remains connected to the lamp driver for the note E byvirtue of the strapping of the middle and lower contactors associatedwith the lower contactor 48-3 of the switch designated F. As the studentproduces tones the lights for all of the notes in their natural statewill light on the display board in the positions corresponding to thosein the music from which the student is reading the notes. When thestudent reads the notes on the lower space of the staff and providing heremembers to produce the tone F sharp the small lamp on the displaypanel for the note F sharp will not be lighted, but instead the lamp onthe space for the note F will be lighted and this lamp, corresponding inlocation on the display board to the position of the note that thestudent has read from the music will indicate to the student that thecorrect tone has been produced. if instead the student incorrectlyproduces the tone for the note F natural, the lamp E+ will be lighted asan indication that the student has not remembered to produce the F sharptone.

The key signature containing two sharps has the second sharp on the noteC and for aiding a student reading from music having this key signature,the switches for the notes F and C should both be operated to theirsharp position. The switch C in its sharp position, with its contactorsmoved to their lower contacts changes lamp circuit routings for thenotes C sharp, C and 8+ corresponding to the changes in routing made bythe switches relative to the notes F sharp, and D+.

The key signature containing three sharps has the third sharp on thenote G and for assisting a student reading from music having this keysignature, the switch G would be operated to its sharp position inaddition to those for the notes F and C. At the upper contactor 48-1 ofthe switch G the path from the lamp driver 32 associated with the Gsharp filter is now routed to the lamp 42 for the note G, the G sharplamp being disconnected. The lamp driver 32 associated with the filterfor the note G is routed to the lamp for the note F sharp which wasdisconnected from the F sharp lamp driver by the F switch. If now, inreading the music and producing tones correctly including F sharp, Csharp and G sharp the lamps corresponding to the positions of the notesF, C and G on the staff will be lighted in response to F sharp, C sharpand G sharp, these being the lamps designated F, C, and G. If instead,the student produces the natural of any one of these notes, the resultwill be the lighting ofa lamp behind one of the small apertures nextbelow the lamp which should have lighted.

Turning now from key signatures employing sharps to key signaturesemploying flats, the key signature containing one flat has the symbolassociated with the note B. The adjust the device for this keysignature, which represents the key of F Major, the contactors 48-1,48-2 and 48-3 of the switch B are moved to their upper position allother switches being left in their natural settings. With the switch Bso adjusted, the lamp driver 32 associated with the filter for the noteB flat is disconnected from the B flat lamp at the contactor 48-3 and isconnected instead to the B lamp. At the middle contactor 48-2 of theswitch B the lamp driver 32 for the note B filter is connected to thelamp B+. Correct sounding of the note B flat by the student will resultin the lighting of the lamp for the note B at the point on the staff onthe display board corresponding to the point from which the student isreading the note. If instead, the student erroneously sounds the note B,the B+ lamp will be lighted. The key signature containing two flats hasthe second flat associated with the note E and the setting of the switchE to the flat condition will associated the lamp E with the lamp driverfor the note E flat and will associate the lamp E+ with the lamp driverfor the note E. The key signature containing the third flat has thatflat associated with the note A. With the switch A set in its flatinsertion position, the contactors being moved upwardly, the path fromthe lamp driver for the note A flat is traced through the contactor 48-2and middle contact of the switch G and the lower contactor 48-3 andassociated upper contact of the switch A to the lamp A. The path fromthe lamp driver 32 for the note A is traced through the middle contactor48-2 and associated upper contact of the switch A to the lamp for thenote B flat, which was disconnected at the lower contactor of the switchB, now operated to its flat insertion position. If the student correctlyproduces the note A flat when reading it, the A lamp will light. If thestudent incorrectly produces the tone for the note A instead of A flat,the lamp for A sharp (B flat) will light, and this is one of the lampslocated behind a small window or aperture. It will be apparent that theobjective of the sharp-flat insertion keys is to adjust the device sothat for any key signature, the notes properly sounded will cause thelighting of lamps in the locations on the lines and spaces of the staffthat the notes actually appear in the music from which the student isreading.

As mentioned hereinbefore, the sixth and seventh sharps in the keysignatures of sharps are associated with the notes E and B, which haveonly semi-tone interval relationships to the notes F and C respectivelynext above them. Also, as mentioned hereinbefore, the correct responseto the reading of E sharp is the sounding of the note F and the correctresponse to the reading of the note B sharp is the sounding of the noteC. The B switch will accordingly be placed in its sharp condition withthe contactors moved downwardly only after all of the other switcheshave been placed in their sharp conditions. With both the C and Bswitches in their sharp conditions the operating path from the lampdriver 32 associated with the note C is traced through the middlecontactor 48-3 and associated lower contact of the switch C, and theupper contactor 48-1 and associated lower contact of the switch B to thelamp B. The lamp C is disconnected at the middle contactor 48-2 of theswitch C and a path is extended from the lamp driver 32 associated withthe filter for the note B through the lower contactor and lower contactof the switch C and the middle contactor and associated contact of theswitch B to the lamp A sharp-B flat. Thus, if the student, in reading Bcorrectly produces the tone for C which is the same as B sharp the lampdriver 32 of the C filter will cause the lighting of the lamp B. Ifinstead, the student produces the note B, the lamp for A sharpB flatwill be lighted instead.

The extreme case in the case of flats is, as previously set forth, thekey signatures having 6 and 7 flats in which the flats are associatedwith the notes C and F respectively. Assuming the student is readingmusic having a key signature of seven flats, all of the switches wouldhave been set in their flat conditions with their contactors movedupwardly. With the switches in this condition and referring to theswitch F, the lamp operating path is traced from the lamp driver 32associated with the note E through the lower contactor 48-3 of theswitch F and its upper contacts to the lamp F, the path from the lampdriver 32 associated with the note F is traced through the middlecontactor and its upper contact of the switch F to the lamp F sharp Gflat and the path from the lamp driver associated with the note F sharpG flat is traced through the upper contactor of the switch F from whichpath is extended by virtue of the strapping together of the middle andupper contacts to their lower contactors of the switch G and itsassociated upper contacts to the lamp G. Thus, the production of thetone E, which by virtue of the key signature is now called F flat, willresult in the lighting of the lamp F, the production of the tone F willresult in the lighting of the lamp G flat-F sharp which is locatedbehind one of the small apertures or windows, and the production of thenote G flat will result in the lighting of the G lamp.

There remains for consideration the utility of the transposingmulti-path plug-and-jack set 40. It will be supposed that a singerdesires to sing a musical composition which is written in the key of CMajor and that the composition includes as its highest note the note Eabove high C, which appears in the fourth space of the treble clef butthat the highest note that the singer can effectively sing is B belowmiddle C which is on the third line of the treble staff. The singer musttranspose downwardly into another key, but in order to enable him to beguided in doing this by reading from the music written in the key of CMajor the bank of lamps must be shifted downwardly by disconnecting andreconnecting the plug-and-jack set 40 a distance equivalent to fivesemi-tones, so that when the singer produces the tone for B below middleC the lamp for E will be lighted. in the scale of C Major, E is the notecalled *mi" and C is the note called do." In transposing downwardly Bbecomes mi" for the singer and G becomes do." Accordingly, thetransposition is to the key of G Major which has one sharp on F. Withthe transposition made so that the C lamp is under the control of thelamp driver circuit 32 associated with the G filter the B lamp will beunder the control of the lamp driver 32 associated with the filter forthe note F sharp. Following downwardly, the tone E produced by thesinger will cause the lighting of the A lamp, the note D will cause thelighting of the G lamp the note C will cause the lighting of the F lampand as already noted, the note B will cause the lighting of the E lamp.Be cause the Eland 8+ lamps become associated with lamp driver circuitsonly when certain of the sharp-flat insertion keys are in thenon-natural positions those additional lamps in the bank of lampsintroduce no problems in a transposition effected at the plugand-jackset 40.

Male vocalists usually sing an ocatave below the written musicalnotation of the melody, and thus the tones produced by them would bepassed by filters for notes associated with the bass clef staff. Inorder that the vocalist need not learn to recognize the notes of thatstaff, a full octave downward transposition of the lamps relative to thelamp drivers may be made, so that the music, if correctly read and snug,although sung an octave lower, will cause the lighting of lamps on thetreble clef display panel, thus matching the written music.

Mention was made previously of instruments that sound in a different keythan the key of C. An example of such an instrument, also as previouslymentioned, is the B flat clarinet which sounds in the key of B flat whenthe musician reads from music written in the key of C Major and fingersthe instrument as he has been taught for that key. By shifting the lampbank relative to the lamp drivers 32 so that the lamp C is aligned to becontrolled through the B flat filter and its associated lamp drivercircuit 32 the playing of the notes of the B flat major scale willresult in the lighting of only the lamps behind the larger windows onthe display board, which represent the notes on the lines and spaces ofthe staff thereby informing the instrumentalist that he is correctlyreading and playing his sheet music and correctly fingering hisinstrument.

Let it be supposed instead that a C instrument is to play in unison withB flat clarinet and that the only sheet music for the composition thatis available to the two instrumentalists is written in the key ofCMajor. It will further be supposed that the carinetist will play in hisconventional manner from the music, the instrument sounding in B flat.It thus will be necessary for the other instrumentalist to transposedownwardly from the C Major to B flat Major, which is a downwardtransposition of two semi-tones. By repositioning the plugs and jacks ofthe transposing plug-and-jack set 40 downwardly two semi-tone steps, tobring the C lamp under the control of the lamp driver 32 associated withthe filter 30 for the note B flat the C instrument, played bytransposition in the key of B flat, which includes the notes B flat andE flat instead of B natural and E natural, or the transposinginstrument, manipulated in the key of C Major without transposition, orboth playing together will cause the lighting of the same lamps, andthese lamps will be the ones occupying positions on the lines and spacesof the display board.

It will be apparent that use may be made of the transposingplug-and-jack set 40 as an aid to the solution any problems arising intransposing from one key to another. Each step of transposition betweenthe plug-andjack components of the transposing plug-and-jack set 40 awayfrom a one-for-one relationship between the tone filters 30 andcorrespondingly designated lamps 42 in the lamp bank brings the filterscomprising a different major key into association with the lamps on thelines and spaces of the treble staff on the display panel. All of theseven key signatures containing sharps and all of the seven keysignatures containing flats may be achieved by transposition of thelamps 42 relative to the filters and their associated lamp drivercircuits 32.

It may be noted that transposition could be accomplished in another way,namely, by rearranging the lamps and their aperatures and having therepresentation of the musical staff movably positionable with respect tothe lamps. With such an arrangement the representation on the panel of atreble clef staff and/or a bass clef staff could be shifted upwardly ordown wardly. For example, referring once again to the B flat clarinet,the display panel could be moved downwardly to present the third spaceon the staff in front of the B flat lamp.

Attention is now directed to the switch comprising the swingers 14 and20 for selecting either the ramp preamplifier 16 or the wide passpreamplifier 18 for inclusion in the input to the device. With the widepass preamplifier switched into the input the second and perhaps fourthharmonics of some of the tones, if within the overall range of thedevice, and if of sufficient amplitude, may pass through filters one ormore octaves above the filter of the fundamental and operate two or moreof the lamp driver circuits to light two or more of the lamps. Harmonicswhich are power-of-two multiples of the fundamental fall exactly onoctave distances from the fundamentals, whereas odd numbered harmonicsand even numbered harmonics which are not power-of-two multiples of thefundamental do not coincide with octave related harmonics of thefundamentals, and in the equal tempered scale the frequencies of noteswithin an octave generally do not match the frequencies of the odd orthe non-octave related even harmonics. However, in some instances thefrequency of a harmonic which is not a power-of-two multiple of afundamental will be sufficiently close to that of an unrelated note thatthe filter for that note will pass the harmonic.

When the ramp preamplifier is switched into the input circuit instead ofthe wide pass preamplifier, because it has a rising attenuation withrising frequency, and the energy in the harmonics, being less than theenergy in the fundamentals, the harmonics will be suppressed and lampsrepresenting harmonics will not be lighted. Also, if two or more notesare simultaneously impressed on the microphone, all but the lowest maybe attenuated to such an extent as to be incapable of activating itslamp driver circuit. The only circumstance in which the lighting of twolamps is likely to occur in response to a signal tone is that the toneis out of tune and has a frequency at or near a mid-point between thefrequencies of two successive notes in the chromatic scale. When thisoccurs the lighting of two adjacent lamps is possible.

It will be apparent that with the device embodying the presentinvention, direct indication and identification of an unknown tone ornote, without any comparison, is achieved. Thus it becomes possible toidentify not only individual unknown tones but also the components ofchords or other combinations of tones simultaneously sounded. Also it ispossible to identify the components of sounds other than purely musicaltones, such as for example the pitch and inflection in speech.

Attention is now directed to FIG. 5 for details of the ramp amplifier16, the saturating amplifier 22 and other components. In FIG. 5 a dottedline rectangle containing the circuitry of the ramp preamplifier hasbeen identified by the reference numeral [6 to correspond to FIG. I anda second dotted line rectangle encloses the portion of the circuitrywhich is the saturated amplifier and this rectangle has been designatedby the reference numeral 22 in correspondence with FIG. 1. As shown inFIG. 5 the ramp preamplifier comprises five stages in cascade. thestages being identified by the referenc: numerals 70, 72, 74, 76 and 78.Each of the five stages of the ramp preamplifier is an audio frequencyamplifier which may include one or more discrete transistor componentsbut which preferably is an integrated circuit device providing thedesired gain. Each of the five stages has associated with it a feedbacknetwork from the output to the input comprised of resistive andcapacitive components. In the case of the first stage 70 the feedbacknetwork comprises resistor 71 paralleled by a capacitor 73, and it isthe purpose of this network to attenuate frequencies above the highestfundamental that the device is required to identify which, as will beset forth hereinafter, will probably be slightly below 1,000 cycles persecond. Each of the other four stages has a feedback network from outputto input comprised of two parallel branches, one branch comprising aresistor and the other branch comprising a resistor and a capacitor inseries. In the case of stage 72 the three components of the feedbackpaths are identified by the reference numerals 75, 77, and 79respectively. The values of the components in the feedback networks areselected to give each stage a roll-off of approximately 6 db per octave,so that over the four stages there is a roll-off in the form ofincreasing attenuation with increasing frequency, of the order of l8 to24 db per octave. It follows from this that an overtone one octave abovea fundamental, and variously designated as a first harmonic or as asecond harmonic when the fundamental is considered to be a firstharmonic, will be attenuated at least 18 db. An overtone two octavesabove the fundamental will be attenuated at least 36 db. The result isthat a fundamental impressed upon the input to the ramp preamplifier atthe same level as a fundamental an octave below it will appear at theoutput 19 db below the output level of the lower of the twofundamentals.

The interstage coupling is frequency relative, typified by capacitor 80and resistor 82 from stage 70 to stage 72, pure resistive, comprisingthe resistors 84 and 86 from stage 72 to stage 74, reactive from stage74 to stage 76, and reactive from stage 76 to stage 78. The values ofcomponents in the reactive couplings are chosen to attenuate frequenciesbelow the lowest fundamental to be handled by the system.

For utilization in a device for giving visual indication in the humanvoice range, or the range of notes of the grand staff in musicalnotation, a frequency range of four octaves is considered to beadequate, including as its lowest note a frequency of 65.41 cycles persecond (Hertz) which is the frequency of the note C two octaves belowmiddle C and having as its highest note a frequency in the neighborhoodof L000 cycles per second, the note that ends the octave which beginswith the C next above middle C having a frequency of 987.8 cycles persecond. In a particular embodiment of the invention the parameters ofthe ramp preamplifier are such that the amplitude at the output of thefifth stage, designated 78, will be about the same for the highestfrequency as the signals fed into the input of the first stage,designated 70, from a transducer, such as a microphone, and it followsfrom this that lower notes impressed upon the input at the sameamplitude will have a higher amplitude at the output in correspondencewith their frequency as determined by the previously mentionedattenuation of ascending frequencies at a minimum of 18 db per octave.In a specific embodiment of the invention, for utilization by thecircuitry connected to the output of the ramp preamplifier a minimumoutput signal of 3 millivolts is adequate and this might be the same asthe input from a directly connected microphone.

Whereas, in the diagrammatic showing in FIG. 1, a microphone I0 isconnected to the input of the ramp preamplifier 16 through an amplifierl2,jacks and I02 (FIG. 5) are shown connected directly to the input tothe ramp preamplifier. A microphone may be connected by a suitable plugthrough one of the jacks and another source of sound waves, such as atape player, may be connected through the other jack. FIG. 5 contains noshowing of an amplifier corresponding to the amplifier 12 in FIG. I, itbeing understood that microphones and reproducers of recorded sound havevarying output voltage depending upon their types and that for somepurposes no amplification will be needed between the sound source andthe input to the ramp amplifier l6 and that if amplification is neededit may be supplied.

Mentioned has been made previously of the fact that the coupling betweenstages 72 and 74 of the ramp preamplifier is purely resistive, whereasthe interstage couplings between all other stages include a capacitorwhich, of course, offers different impedances to different frequencies.The coupling between stages 72 and 74 comprises a voltage divider whichis non-reactive from a frequency standpoint and its purpose is to applyto stage 74 only a fraction of the voltage appearing at the output ofstage 72 in order to avoid overloading of the remaining three stages andattendant distortion of signals passing through those stages.

The output of stage 78 of the ramp preamplifier is coupled throughresistor 106 to the input of saturated amplifier stage 22 the amplifyingcomponent of which is indicated by the conventional triangular symbol108 for an amplifier and this may be an integrated circuit component.The bias on the amplifier component 108 is adusted so that the amplifierwill operate between saturation and cutoff at the highest frequency thatthe set of tone indentifying filters is intended to recognize and it hasbeen mentioned previously that the output of the last stage of the ramppreamplifier 16 may be of the order of 3 millivolts for that frequency.It follows from this that the output of the saturated amplifier 22 willbe a square wave for all signals impressed upon the input of the ramppreamplifier 16. Because of the attenuation characteristics of the ramppreamplifier as set forth hereinbefore, namely that it attenuatesfrequencies on an ascending basis at a roll-off rate of at least l8 dbper octave the lowest of any two or more frequencies impressed upon theinput to the ramp amplifier at the same time, whether they are two ormore fundamentals, a fundamental and one or more harmonics or more thanone fundamental with its harmonics, the lowest frequency passing throughthe ramp preamplifier will have the greatest amplitude at the output ofthat amplifier. Even though the harmonics may at the input exceed inamplitude the fundamental, which is a situation that may occur in thecase of certain types of musical instruments and is likely to occur inthe case of sung musical notes or speech, the roll-off of the ramppreamplifier will provide for predominance of the fundamental at theoutput of the ramp preamplifier from the standpoint of amplitude. If, asis also probable, a funda mental and one or more harmonics shouldcombine to produce a resultant wave, the resultant will cross the zeroaxis of the wave at the same rate as the fundamental so that itsenvelope will have a configuration corresponding to the frequency of thelowest note passing through the ramp amplifier. With the saturatedamplifier 22 operating between saturation and cut off it will conductwhile the wave impressed upon it by the ramp preamplifier has onealgebraic sign and will cut off while the wave has the other algebraicsign, with the result that the output of the saturated amplifier will bea square wave at the frequency of the lowest sinusoidal wave impressedupon the input of the ramp preamplifier.

The output of the saturated amplifier 22 is connected to acommon-emitter transistor amplifier stage 120 which has connected acrossits base-emitter junction a diode 122 poled oppositely relative to thepolarity of the normal biasing potential for that junction in the typeof transistor indicated, namely an NPN transistor. The diode 122 limitsthe reverse bias potential that can develop across the base-emitterjunction of the transistorv The output of the transistor stage 120 isconnected through a resistor 124 to one of the terminals of asingle-pole double-throw switch 126 mounted on control panel 104. Theoutput of the transistor 120 is also connected to the input of afrequency divider 128, the output of which is connected through aresistor 130 to the other terminal of the switch 126. The frequencydivider 128 may be an integrated circuit device and in essence itcomprises a bistable flip-flop that may be switched from one stablecondition to the other only in response to input transitions of onepolarity. Thus it changes from one stable state to the other only inresponse to alternate transitions in a square wave applied to its input,so that its output is a square wave at half the frequency of the input.The reason for the provision of the frequency divider will be describedfollowing completion of the description of FIG. 5.

The swinger or contactor of the single-pole switch 126 is connected tothe input of a common-emitter amplifier stage comprising the transistor134 which has its collector connected for base-collector biasingpurposes through a resistor 136 and the collector-emitter junction of atransistor 138 to a voltage source at positive polarity. For outputpurposes the collector of the transistor 134 is connected to the inputsto the several fre quency pass filters 30 in FIG. 1 and the connectionbetween the output electrode of the transistor 134 and the filters 30may be considered as including the swinger and upper contact of thesingle-pole doublethrow switch in FIG. 1. With the circuit shown in FIG.5, the frequencies appearing at the output of the saturated amplifier 22will be impressed on the filters if the contactor of switch 126 isengaging its righthand contact, thus bypassing the frequency divider128, and tones at one half the frequencies emitted by the saturatedamplifier 22 will be impressed upon the filters 30 if the contactor ofswitch 126 engages its left hand contact, which is connected to theoutput of the frequency divider 128.

Returning to consideration of the transistor 138 its base is connectedto the contactor of a potential divider 144 for supplying a potentialpositive with respect to ground to the base of the transistor 138. Thepotential divider 144 is located on the control panel 104. Its functionis to control through the transistor 138 the biasing potential on thecollector of the transistor 134 and thus to control the gain of thetransistor 134. Thus, the potential divider 144 and the transistor 138cooperatively serve as a gain control for the transistor 134 but inactuality they serve as a bandwidth control for the filters 30 will bedescribed hereinafter.

Consideration will now be given to the utility of the frequency dividerand the arrangement for bypassing it in a device as represented in HQ.5. It will be remembered that mention has been made previously ofproviding for the recognition of frequencies in a range of four octaves,beginning at the low end at slightly about 62 cycles approximately andending just below 1,000 cycles approximately. Four octaves of thechromatic scale involves a total of 48 discrete tones which, on a basisof direct routing of tones from the saturated amplifier 22 to thefilters 30 would require a total of 48 filters. However, tones in thethree octaves from approximately to approximately 1,000 may, by passingthem through the frequency divider, be recognized by three octaves offilters tuned from approximately 62 cycles per second to approximately500 cycles per second. It would be appropriate to identify each filteron the display panel by a designation one octave above it, so that thedesignations of the notes on the display panel would correspond with thefrequencies impressed on the input to the ramp preamplifier but passedthrough the frequency divider. Then, in order to provide foridentification of tones below 125 cycles the switch 126 on the controlpanel 104 would be operated to the position to bypass the frequencydivider 128. Tones below 125 cycles and other tones up to 500 cycleswould be identified by the set of 36 filters required to cover threeoctaves and it would be understood by the user of the device that withthe switch in this position each lamp designation on the display panelwould be one octave higher than the note actually causing the lightingof the lamp. With this arrangement, four octaves of notes may beidentified individually using three octaves of filters. It will beunderstood that the frequency range hereinbefore suggested is merelyillustrative of the principles involved, and the device is adaptable toany portions of the audible sound spectrum.

Reference was made previously to the fact that potentiometer 144, whileserving as a gain control for the saturated amplifier stage 134,actually serves as a bandwidth control for the filters 30. In order toexplain this, attention is directed to FIG. 6 which is a family ofcurves of typical frequency response ofa filter at different inputlevels. In FIG. 6 output levels are plotted along the vertical axis andfrequency is plotted along the horizontal axis. The curves representingoutput levels for the different input levels are generally symmetricalabout a line fl, which is the midpoint of the pass band of the filter,and the output level is generally a maximum at that frequency. It willbe observed that at higher input levels, which produce higher maximumoutput levels at the mid-frequency, the output level curves begin torise earlier and fall away later in the ascending sound frequencyspectrum.

The line V, represents a predetermined output level crossing all of theresponse curves. It will be noted that response curve R which is thelowest of the three in terms of maximum output intersects response curveR at frequencyf below f and atf, above 11,. Response curve R intersectsthe output level line V at frequency f which is below frequency f, andat frequency f; which is above frequency f, I Response curve Rintersects output level line V, at f which is below f and atf; which isabove f v Thus at output level V, an input level that gives an outputresponse curve R has a pass band from f, tof, v an input level thatprovides the response curve R has a pass band f to f,, t and the inputlevel that provides the response curve R has a pass band from to f Thelamp driver stage comprising the transistor 34 may be biased to have athreshold or a trigger level below which the lamp shows no illumination,with the lamp beginning to glow dimly at the threshold level and comingto full brightness at a somewhat higher input than the threshold levelbut preferably appreciably before fl, is reached. V in FIG. 6 may beconsidered as representing the threshold input potential for the lampdrivers. With the gain control 144 for the saturated amplifier set at alevel corresponding to the response curve R the lamp associated with afilter will show illumination atf, and the lamp will show illuminationin the band between the frequencies f and f If the gain of the saturatedamplifier is increased to a level which will produce the response curveR the lamp will be illuminated in response to any frequency in the bandbetween frequencies f and f A still further increase in the output ofthe saturated amplifier will provide for illumination of the lampbetween a still wider band of frequencies such as represented by theband between frequency fl and f The variable bandwidth feature hasutility particularly in the training of beginning voice students whohave difficulty in producing with accuracy various musical tones. With awide bandwidth adjustment of the apparatus the student can discover evenwith an inaccurately produced tone that he is off but near the desiredtone and he can easily discover that he needs to pitch higher or lowerin order to reach the tone. As the student becomes more experienced thebandwidth may be reduced by reducing the gain of the saturated amplifierso that the system will tell him at once whether he is on or nearly onthe correct pitch.

With the saturated amplifier and the bandwidth control, the operation ofthe lamps is entirely dependent upon what frequency is being played orsung into the microphone and not how loudly the person is playing orsinging. The bandwidth control can be set so that two lights will comeon if the student is playing or singing a note that is halfway betweenthe frequencies represented by the two lamps. It may also be adjusted bycutting back the gain of the saturated amplifier so that neither of twolamps will show illumination until the student has produced a tone thatis close to the one represented by a lamp that lights. This forces thestudent to learn to produce the notes precisely and if he is very faroffin either direction from the desired frequency no lamps will belighted.

FIG. 7 shows typical circuitry for the filters, which are indicated inFIG. 1 without circuitry by the reference numeral 30 and by designationsof frequencies of slightly more than one chromatic octave, occupying inmusical notation the lines and spaces of the treble staff. Reference wasmade hereinbefore to a published article describing the design of activeband pass filters. A filter configuration that is shown therein, and iscalled a multiple feedback band pass filter is shown in typical form inFIG. 6. The multiple feedback active band pass filter has been enclosedin a dotted line rectangle in FIG. 7 to which the reference numeral 30has been applied. The inputs of all of the filters 30 may be connecteddirectly, as shown in detail in FIG. 5, to the circuitry associated withthe output of the saturated amplifier 22, or through the switch 20 shownin FIG. 1. In the schematic showing in FIG. 7 the filter input includesa voltage divider comprising resistors and 152. From the junction ofthese resistors the output signals from the bandwidth control transistor134 in FIG. 5 are applied through capacitor 154 to the input of an audioamplifier contained in an integrated circuit component representedconventionally by a triangle designated by the reference numeral 156.The output of each filter is connected to a lamp driver circuitindividual to the filter, the lamp driver circuit being shown in FIG. 3of the drawings and the transistor 34 of that circuit being also shownin FIG. 6.

Feedback is taken from the output of the filter 30 in two paths, onebeing resistive only and feeding back directly to the input of theamplifier I56 and the other being capacitive only and being applied tothe input to the amplifier 1S6 ahead of the capacitor I54, namely at thejunction of that capacitor with the dividing point of the signalattenuating potential divider comprised of the resistors 150 and I52.The capacitive branch of the feedback contains the capacitor 158. Theresistive branch includes a variable resistor and a fixed resistor 162in series. With the circuitry shown in FIG. 7, filters having high Q andcapable of responding individually to the tones of the chromatic scalemay be produced inexpensively and in compact form. In an embodiment ofthe invention having filters employing the circuitry shown in FIG. 7 thefilters have a Q of approximately 35.

FIG. 7 includes a schematic circuit diagram of an arrangement forindicating visually by means of a meter the percentage deviation, ifany, from the nominal or peak frequency of the filter of a tone beingpassed through any of the filters. It is operative upon the principlethat the output wave of any of the filters, when the filter is passingthe exact frequency to which it is tuned has a phase difference relativeto the input wave of If the phase difference is less than 180, the tonepassed by the filter is flat relative to its peak frequency whereas ifthe phase difference exceeds 180 the tone passed by the filter is sharprelative to the peak frequency of the filter.

The circuit that controls a meter to indicate deviation of the tone fromcorrespondence with the peak frequency of the filter is a phasedetector. As indicated in FIG. 7 an output is taken from each filter, inaddition to the output to the lamp driver circuit, to one of threeconductors designated by the reference numerals I70, I72 and 174. In thescale succession of filters, whether diatonic or chromatic, the filtersare connected to the three conductors 170, I72 and 174 in rotation sothat adjacent filters in the frequency spectrum shall not be connectedto the same output lead.

Conductors 170, 172 and 174 extend to the inputs of amplifiers 176, 178and 180, respectively. and the outputs of these three amplifiers areconnected in parallel to the input of an amplifier 182. The output ofthe amplifier 182 is connected to the triggering input of a bistablefiip-flop 186. The input bus for all of the filters is connected by aconductor 188 to the triggering input of a bistable flip-flop 190.

Each of the bistable flip-flops 186 and 190 is arranged to switch backand forth between it two states in response to like input transitions.Thus, it functions as a frequency divider. The outputs of the twoflip-flops 186 and 190 are connected to an exclusive OR gate designatedgenerally by the reference numeral 192 and consisting of four NAND gates194. The truth table for the exclusive OR gate may be expressed in theterms that when the inputs to the gate 192, which are the outputs fromthe flip-flops 186 and 190, are alike, whether it be binary O or binaryl, the output of the gate will be binary 0. Conversely, when eitherinput to the gate is binary and the other is binary l the output of thegate will be binary l.

The output of the exclusive OR gate 192 is connected to the junction ofresistors 191 and 193 which are part ofa series circuit between avoltage source and ground, this series circuit including variableresistor 195 and meter 197, the meter being shunted by an integratingcapacitor 199.

The variable resistor 195 serves as part of a multiplier for the meter197 and with the output of the OR gate set in the binary 0 condition thevariable resistor 195 may be adjusted to set the meter at apredetermined reading such as mid scale. When a tone matching the peaksetting of a filter is passed through the filter, the input wave will beimpressed upon the flip-flop 190 and the output wave will be impressedupon the flip-flop 186 and because of the l80 phase difference betweenthe two waves the output of the OR gate will switch back and forthbetween binary 0 and binary l at a uniform rate. The capacitor 199 willabsorb the voltage swings at the output of the OR gate and the meter 197will maintain a steady deflection. Conversely, ifa wave which is of adifferent frequency than the resonant frequency of one of the filterspasses through that filter, there will be a phase difference between thewaves applied to the inputs to the flip-flops 186 and 190. This phasedifference will cause the output of the OR gate to spring back and forthbetween binary O and binary l at unequal rates or intervals and themeter 197 will be deflected from its steady state position. The scale ofthe meter may be calibrated in percentage of phase difference betweenthe input and the output waves to the filter which will indicate thepercentage deviation of the tone from the resonant frequency of thefilter. The circuit shown in FIG. 6 will reveal very small percentagedeviations of tones and thus will indicate to the person using thedevice deviations that would not be indicated by the lighted lampassociated with the filter.

Reset terminals for the flip-flops I86 and 190 are connectable to groundthrough a switch 189 which may be closed momentarily for the purpose ofsetting the two flip-flop circuits to like output conditions and theinputs to the OR gate 192 are connectable to a reset potential through aswitch 187 to set the two inputs to the OR gate in the same condition.The switches 187 and 189 may, if desired, be ganged to comprise adouble-pole double-throw switch.

Attention is directed to the resistors 163 and 164, in series,connecting to one of the amplifiers 170, 172 and 174 the output of thefilter 30 that is tuned to the highest frequency with capacitor 165connected from the junction of the resistors to ground, to the resistor166 connecting to one of those amplifiers the output of the filter 30that is shown in detail in FIG. 7, and which is representative of anyexcept the highest and lowest frequency filters; and to the resistor 167shunted by capacitor 168 connecting to one of the three amplifiers theoutput of the filter 30 that is tuned to the lowest frequency. Thecapacitor 165 in combination with the resistor 163, and the capacitor168 in combination with the resistor 167 provide compensation for thelack of filters tuned to higher and lower frequencies. The filtersbetween the highest and lowest require no such compensation.

The sound identifying device hereinbefore described is usable in variousways for teaching purposes. The, simplest of course, is to have astudent sing or play a musical instrument into the microphone andobserve the lighting of lamps as the tones are produced. In the case ofa musical instrument the student learns the fingering or other method ofproducing the various tones and determines by observing the lighting ofthe lamps, whether or not he is actually producing the intended tones.In the case of the vocalist it is a matter of learning, by hearing hisown voice, to produce tones corresponding to those of the musical scale.In either case, the training may also involve sight reading of music inthe production of tones to correspond with the musical notations.

A system has been devised involving the use of supplementary aidsincluding lesson material. a tape deck at least capable of playingprerecorded tape, and in addition a set of headphones. FIG. 8 shows aschematic circuit for associating the supplementary components with thetone identifying device. In FIG. 8 the microphone jack 100, whichappears on the control panel 104 as in FIG. 5, is connected over aconductor 200 which appears only as a stub in FIG. 5, to the input of anamplifier stage 202. The output of the amplifier stage 202 is connectedthrough a variable resistor 204 serving as a volume control, and througha resistor 206 to an amplifier stage 208. The output of the amplifierstage 208 is amplified by transistors 210 and 212 and the output oftransistor 212 is connected to a jack 214 into which a pair ofheadphones may be plugged. The purpose in providing a pair of headphonesis that the student shall hear the tone vocally produced by him throughthe set of headphones rather than directly from mouth to ear through theair. Since the jack is connected to the input of the tone identifier asshown in FIG. 5, the tone identifier will operate to display visually tothe student the identification of the tone that he has produced.

For the purpose of providing lesson material. a tape player (not shown),which may be a reel-to-reel deck or a cassette device, and arrangedeither to reproduce only or to record as well as reproduce, providedwith a tape containing lesson instructions, may be plugged into the jack220. This jack is connected to the input of an amplifier stage 222 andthe output of this stage is connected to a variable resistor 224 servingas a volume control. The volume control 224 is connected through aresistor 226 to the input to amplifier stage 208 in parallel with themicrophone path, and thus the student will hear in the headphones theinstructions which comprise the lesson, and which may be entirely verbalor may include tones that the student is to imitate. The tape maycontain appropriate silent intervals during which the student respondsto the instructions by singing into the microphone or performing anyother acts as directed. It is also contemplated that there may beprovided printed lesson material to be viewed by the student as helistens to the recorded instructions and acts upon the directionscontained in the tape, the printed lesson material containing suchrelated visual material as music staffs whereon appear in their properplaces the notes that the student is instructed to sing.

A further possibility in connection with the teaching procedurehereinbefore described is the provision of a tape playing machinegenerally of the type called a stereo player, and having on the tape twotracks, one containing instructions and tonal material that the studentis to hear in the headphone set. The other contains tonal material to beimpressed upon the input to the sound identifying device. The track thatcontains the material that is to be impressed upon the tape identifyingdevice may have its output connected to the jack 102 in FIG. which, aspreviously described is an alternate input to the ramp preamplifier.

It may under certain circumstances be desirable to record an entirelesson period, including all of the instructions to the student as wellas his responses. For that purpose an output is taken from the amplifierstage 208, paralleling the output that goes to the transistor 210, to avolume control 230. The volume control feeds signals to a jack 232 andthere may be plugged into this jack a tape recorder, either reel-to-reelor a cassette recorder, which would be in operation during the lesson torecord it in its entirety, so that the student may later, and ifdesired, repetitiously listen to his performance in the teaching period.

A system such as that depicted in FIG. 8, employing the tone identifierunit with the supplementary units comprising a head set and a tapeplayer may be employed for speech analysis and for the correction ofspeech defects as well as for sung or played musical tones. It may beused to diagnose vocal disorders and test total pitch range andintensity levels, to improve and correct pitch and intensity levels, toaid in the training of persons with impaired hearing, to develop fulluse of pitch range, and to learn intonational patterns. In addition tousage by therapists in the treatment of patients having speech problems,the system may be used by public speakers and actors to discover andcorrect undesirable speech habits. Since, with the ramp preamplifierincluded in the sound identifying unit, only fundamentals of speechtones are indicated by the set of lamps, the device may be used as aguide for pitching speech in desired areas of the sound spectrum. In theusage of the system for therapeutic purposes the tapes to which thepatient listens for training purposes may contain the sounds and wordswhich the patient is instructed to imitate, thereby enabling him toovercome speed difficulties.

It will be apparent that interchangeable display panels may be providedfor association with the device, each arranged to supply toneidentification information in accordance with special requirements. Itwill also be apparent that the device may encompass a range of one ormore octaves or fractions thereof or that it may be arranged to identifytones which are not in sequence of 5 either diatonic or chromatic scale.For example the device may be provided with six filters tuned to thefrequencies of guitar strings and having associated lamp drivers andlamps to provide a device for the sole purpose of tuning guitars. Such adevice may also have, or have instead, filters tuned to the frequenciesto which the strings of all the instruments in the violin family aretuned. A device in accordance with the present inven tion might have asufficient range of tone channels to enable the tuning of electronicinstruments such as electronic organs.

For usage in connection with some types of musical devices, as forexample in the tuning of the strings of an electric guitar or in tuningthe tone generators of an electronic organ it may be desirabletoestablish a direct connection between the output circuitry of theelectronic instrument and the bank of tone generation filters of thetone identifying device, rather than to go through the double conversionof electrical waves to sound waves and the reconversion of thesound'waves to electrical waves through a loud speaking transducerfeeding into the microphone 10. As shown in FIG. 1, there may beprovided an input terminal 24 for connection to the output of any typeof electronic musical instrument, including a tape player or a discrecord player, the alternate input terminal being connected by aconductor 26 to the inputs of all of the tone filters, corresponding tothe connection of the amplifier 22 to the inputs of those tone filters.

What is claimed is:

l. A device for identifying sound waves having different frequencieswhich comprises:

sound wave responsive means;

means comprising filters for separating waves of dif- 4 ferentfrequencies appearing at the output of the sound wave responsive means;means activated by said wave separating means for individually andvisually identifying the sound waves; and means for indicating relativeconformity of said waves with the center frequency of the filters bycomparing the phase of said waves at the input and output of saidfilters. 2. A device in accordance with claim 1 wherein the 50 phasecomparing means comprising digital logic components.

3. A device in accordance with claim 1 wherein the phase comparing meanscomprises:

means for producing a square wave derived from the input of the filterand a square wave derived from the output of the filter;

an exclusive OR gate for combining the two square waves to produce asingle output wave; and means for interpreting the output wave of the ORgate.

imam-i

1. A device for identifying sound waves having different frequencieswhich comprises: sound wave responsive means; means comprising filtersfor separating waves of different frequencies appearing at the output ofthe sound wave responsive means; means activated by said wave separatingmeans for individually and visually identifying the sound waves; andmeans for indicating relative conformity of said waves with the centerfrequency of the filters by comparing the phase of said waves at theinput and output of said filters.
 2. A device in accordance with claim 1wherein the phase comparing means comprising digital logic components.3. A device in accordance with claim 1 wherein the phase comparing meanscomprises: means for producing a square wave derived from the input ofthe filter and a square wave derived from the output of the filter; anexclusive OR gate for combining the two square waves to produce a singleoutput wave; and means for interpreting the output wave of the OR gate.